U.S. patent application number 12/601313 was filed with the patent office on 2012-02-09 for load measuring apparatus, method, and program.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES, LTD.. Invention is credited to Hideyasu Fujioka, Yoshiyuki Hayashi.
Application Number | 20120035865 12/601313 |
Document ID | / |
Family ID | 43010794 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120035865 |
Kind Code |
A1 |
Fujioka; Hideyasu ; et
al. |
February 9, 2012 |
LOAD MEASURING APPARATUS, METHOD, AND PROGRAM
Abstract
A load is based calibrate on data collected under wide
observation conditions and promptly calibrate loads of a plurality
of wind turbine blades. A load measuring apparatus is applied to a
wind turbine in which a pitch angle of a wind turbine blade is
variable. The apparatus includes a sensor for obtaining a
distortion of the wind turbine blade; a load calculating unit
having a function expressing a relation between the distortion of
the wind turbine blade and a load on the wind turbine blade, for
obtaining the load on the wind turbine blade by applying to the
function the distortion based on measurement data of the sensor;
and a calibration unit for calibrating the function based on the
measurement data of the sensor obtained in a pitch angle range and
a rotational speed range of the wind turbine blade in which a
variation between maximum and minimum aerodynamic torques is equal
to or less than a predetermined value.
Inventors: |
Fujioka; Hideyasu;
(Nagasaki, JP) ; Hayashi; Yoshiyuki; (Nagasaki,
JP) |
Assignee: |
MITSUBISHI HEAVY INDUSTRIES,
LTD.
Tokyo
JP
|
Family ID: |
43010794 |
Appl. No.: |
12/601313 |
Filed: |
April 24, 2009 |
PCT Filed: |
April 24, 2009 |
PCT NO: |
PCT/JP2009/058139 |
371 Date: |
November 23, 2009 |
Current U.S.
Class: |
702/42 |
Current CPC
Class: |
F05B 2270/331 20130101;
F05B 2270/808 20130101; F03D 17/00 20160501; Y02E 10/72 20130101;
F05B 2260/83 20130101; F05B 2270/802 20130101 |
Class at
Publication: |
702/42 |
International
Class: |
G06F 19/00 20110101
G06F019/00 |
Claims
1. A load measuring apparatus applicable to a wind turbine in which
a pitch angle of a wind turbine blade is variable, the apparatus
comprising: a sensor for obtaining a distortion of the wind turbine
blade; a load calculating means having a function expressing a
relation between the distortion of the wind turbine blade and a
load on the wind turbine blade, for obtaining the load on the wind
turbine blade by applying to the function the distortion based on
measurement data of the sensor; and a calibrating means for
calibrating the function based on the measurement data of the
sensor obtained in a pitch angle range and a rotational speed range
of the wind turbine blade in which a variation between maximum and
minimum aerodynamic torques due to wind speeds is equal to or less
than a predetermined value.
2. The load measuring apparatus according to claim 1, wherein the
calibrating means calibrates the function based on the measurement
data of the sensor obtained in the pitch angle range and the
rotational speed range of the wind turbine blade in which the
aerodynamic torque is equal to or less than a predetermined
value.
3. The load measuring apparatus according to claim 1, wherein the
calibrating means includes: a table in which the load on the wind
turbine blade in a calm state and a pitch angle and an azimuth
angle of the wind turbine blade are associated with one another; a
load obtaining means for obtaining from the table a load on the
wind turbine blade corresponding to the pitch angle and the azimuth
angle of the wind turbine blade when the measurement data is
obtained by the sensor; a distortion calculating means for
calculating a distortion of the wind turbine blade from the
measurement data of the sensor; and a parameter calculating means
for calibrating a parameter of the function based on the relation
between the load on the wind turbine blade obtained by the load
obtaining means and the distortion calculated by the distortion
calculating means.
4. The load measuring apparatus according to claim 3, wherein the
calibrating means obtains the measurement data of the sensor in the
calm state based on the load on the wind turbine blade obtained by
the load obtaining means and the measurement data of the sensor,
and offset-calibrates the measurement data of the sensor by using
the measurement data in the calm state.
5. The load measuring apparatus according to claim 1, wherein the
sensor includes: a pair of first sensors provided in positions
opposed to each other with the wind turbine blade sandwiched
therebetween; and a pair of second sensors provided in positions
opposed to each other with the wind turbine blade sandwiched
therebetween, the positions different from those of the first
sensors.
6. The load measuring apparatus according to claim 5, wherein the
sensor includes: a pair of third sensors provided in positions
opposed to each other with the wind turbine blade sandwiched
therebetween, the positions different from those of the first and
second sensors and parallel to either of the first and second
sensors.
7. (canceled)
8. A load measuring method applicable to a wind turbine in which a
pitch angle of a wind turbine blade is variable, the method
comprising: obtaining a distortion of the wind turbine blade;
providing a function expressing a relation between the distortion
of the wind turbine blade and a load on the wind turbine blade, and
obtaining the load on the wind turbine blade by applying to the
function the distortion based on measurement data of the sensor;
and calibrating the function based on the measurement data of the
sensor obtained in a pitch angle range and a rotational speed range
of the wind turbine blade in which a variation between maximum and
minimum aerodynamic torques due to wind speeds is equal to or less
than a predetermined value.
9. (canceled)
10. A load measuring method applicable to a wind turbine in which a
pitch angle of a wind turbine blade is variable, the method
comprising: providing a function expressing a relation between a
distortion of the wind turbine blade and a load on the wind turbine
blade, and obtaining the load on the wind turbine blade by applying
to the function a distortion based on measurement data of the
sensor; and calibrating the function based on respective
measurement data of the sensor obtained when the pitch angle is set
to minimum and maximum pitch angles in two points of a first
azimuth angle and a second azimuth angle different from the first
azimuth angle by 180 degrees in a case where a wind speed is equal
to or less than three meters per second.
11. (canceled)
12. The load measuring method of claim 10, comprising: obtaining a
distortion of the wind turbine blade.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is based on International
Application No. PCT/JP2009/058139, filed Apr. 24, 2009, and
priority is hereby claimed under 35 USC .sctn.119 based on this
application. This application is hereby incorporated by reference
in its entirety into the present application.
TECHNICAL FIELD
[0002] The present invention relates to a load measuring apparatus,
method, and program.
BACKGROUND ART
[0003] Generally, in a wind turbine generator, sensors each for
measuring a load applied to a wind turbine blade are attached to a
blade root part and the like, and a load is calculated by
processing data measured by those sensors. However, since the
relation between a load applied to each of the wind turbine blades
and a distortion is not constant due to individual differences
which occur at the time of manufacture of blades and at the time of
attachment of the sensors, there is proposed a method of measuring
a load for each wind turbine blade and calibrating a load value.
[0004] Patent Citation 1: U.S. Pat. No. 6,940,186
DISCLOSURE OF INVENTION
[0005] Conventionally, a load on each wind turbine blade is
measured in a state where a wind turbine rotor is manually fixed so
as not to rotate (using a lock pin or the like) and calibration of
the load is performed.
[0006] However, the calibration work has to be performed for each
wind turbine. To perform calibration on all of wind turbines, the
rotors have to be fixed manually. In a case of a large-scaled wind
firm in which hundreds of wind turbine generators are installed,
enormous work time is necessary. In addition, since the relation
between a load applied to a wind turbine blade and a distortion
varies among wind turbines and wind turbine blades, the calibration
work has to be repeatedly performed on the wind turbine blades. It
takes long time to move a blade to a predetermined position (angle)
by using a turning motor and fix it, and thus the work is not
performed smoothly. There is consequently a problem such that the
work efficiency is low.
[0007] The present invention has been achieved to solve the above
problem, and an object thereof is to provide a load measuring
apparatus, method, and program capable of efficiently calibrating a
load on a wind turbine blade regardless of observation
conditions.
[0008] A first mode of the present invention relates to a load
measuring apparatus applicable to a wind turbine in which a pitch
angle of a wind turbine blade is variable, the apparatus including:
a sensor for obtaining a distortion of the wind turbine blade; a
load calculating means having a function expressing a relation
between the distortion of the wind turbine blade and a load on the
wind turbine blade, for obtaining the load on the wind turbine
blade by applying to the function the distortion based on
measurement data of the sensor; and a calibrating means for
calibrating the function based on the measurement data of the
sensor obtained in a pitch angle range and a rotational speed range
of the wind turbine blade in which a variation between maximum and
minimum aerodynamic torques due to wind speeds is equal to or less
than a predetermined value.
[0009] With such a configuration, the calibrating means for
calibrating the function held in the load calculating means is
provided. The calibrating means calibrates the function based on
the measurement data of the sensor obtained in the pitch angle
range and the rotational speed range of the wind turbine blade in
which the variation between the maximum and minimum aerodynamic
torques due to wind speeds is equal to or less than a predetermined
value. Therefore, the conditions of the wind speed can be
widened.
[0010] In the load measuring apparatus, the calibrating means may
calibrate the function based on the measurement data of the sensor
obtained in the pitch angle range and the rotational speed range of
the wind turbine blade in which the aerodynamic torque is equal to
or less than a predetermined value.
[0011] With the configuration, the measurement data of the sensor
obtained in the pitch angle range of the wind turbine blade in
which the aerodynamic torque is equal to or less than a
predetermined value is used, so that the influence of the
aerodynamic torque can be ignored.
[0012] In the load measuring apparatus, the calibrating means may
include: a table in which the load on the wind turbine blade in a
calm state and a pitch angle and an azimuth angle of the wind
turbine blade are associated with one another; a load obtaining
means for obtaining from the table a load on the wind turbine blade
corresponding to the pitch angle and the azimuth angle of the wind
turbine blade when the measurement data is obtained by the sensor;
a distortion calculating means for calculating a distortion of the
wind turbine blade from the measurement data of the sensor; and a
parameter calculating means for calibrating a parameter of the
function based on the relation between the load on the wind turbine
blade obtained by the load obtaining means and the distortion
calculated by the distortion calculating means.
[0013] As described above, in the table in the calibrating means,
the load on the wind turbine blade in the calm state, the pitch
angle, and the azimuth angle of the wind turbine blade are
associated with one another. The load on the wind turbine blade
corresponding to the pitch angle and the azimuth angle of the wind
turbine blade when the measurement data is obtained by the sensor
is obtained from the table by the load obtaining means. The
distortion of the wind turbine blade is calculated from the
measurement data of the sensor by the distortion calculating means.
The parameter of the function is calibrated by the parameter
calculating means based on the relation between the load on the
wind turbine blade obtained by the load obtaining means and the
distortion calculated by the distortion calculating means.
[0014] Since the load is associated with the azimuth angle and the
pitch angle in the table in the calibrating means, when the azimuth
angle and the pitch angle upon the measurement data being obtained
are known, the load on the wind turbine blade at that time can be
easily grasped. Since the parameter of the function is calibrated
based on the relation between the distortion of the wind turbine
blade calculated based on the measurement data and the load
determined based on the measurement data, the distortion of the
measurement data can be calibrated with high precision.
[0015] In the load measuring apparatus, the calibrating means may
obtain the measurement data of the sensor in the calm state based
on the load on the wind turbine blade obtained by the load
obtaining means and the measurement data of the sensor, and
offset-calibrates the measurement data of the sensor by using the
measurement data in the calm state.
[0016] With the configuration, the measurement data in the calm
state included in the measurement data of the sensor is obtained
and the offset calibration is performed thereon, so that precision
of the measurement data can be improved.
[0017] In the load measuring apparatus, the sensor may include: a
pair of first sensors provided in positions opposed to each other
with the wind turbine blade sandwiched therebetween; and a pair of
second sensors provided in positions opposed to each other with the
wind turbine blade sandwiched therebetween, the positions different
from those of the first sensors.
[0018] With the configuration, the loads in different directions in
one wind turbine blade can be measured. For example, when the first
sensors are provided on the inside and backside of a wind turbine
blade, and the second sensors are provided at the edge side of the
wind turbine blade, the load applied in the direction on the
feather side of the wind turbine blade and the load applied in the
direction on the fine side thereof can be measured by these
sensors.
[0019] In the load measuring apparatus, the sensor may include: a
pair of third sensors provided in positions opposed to each other
with the wind turbine blade sandwiched therebetween, the positions
different from those of the first and second sensors and parallel
to either of the first and second sensors.
[0020] With the configuration, by the third sensors, the apparatus
can be used for measuring information other than a load.
[0021] A second mode of the present invention relates to a load
measuring apparatus applicable to a wind turbine in which a pitch
angle of a wind turbine blade is variable, the apparatus including:
a sensor for obtaining a distortion of the wind turbine blade; a
load calculating means having a function expressing a relation
between the distortion of the wind turbine blade and a load on the
wind turbine blade, for obtaining the load on the wind turbine
blade by applying to the function the distortion based on
measurement data of the sensor; and a calibrating means for
calibrating the function based on respective measurement data of
the sensor obtained when the pitch angle is set to minimum and
maximum pitch angles in two points of a first azimuth angle and a
second azimuth angle different from the first azimuth angle by 180
degrees in a case where a wind speed is equal to or less than three
meters per second.
[0022] With such a configuration, the calibrating means for
calibrating the function of the load calculating means is provided.
The calibrating means can calibrate the function based on the
measurement data of each of the sensors obtained when the pitch
angle is set to the minimum and maximum pitch angles in the two
points of the first azimuth angle and the second azimuth angle
different from the first azimuth angle by 180 degrees in the case
where the wind speed is equal to or less than three meters per
second. Therefore, the function can be calibrated on the basis of a
small amount of measurement data.
[0023] A third mode of the present invention relates to a load
measuring method applicable to a wind turbine in which a pitch
angle of a wind turbine blade is variable, the method including:
obtaining a distortion of the wind turbine blade; providing a
function expressing a relation between the distortion of the wind
turbine blade and a load on the wind turbine blade, and obtaining
the load on the wind turbine blade by applying to the function the
distortion based on measurement data of the sensor; and calibrating
the function based on the measurement data of the sensor obtained
in a pitch angle range and a rotational speed range of the wind
turbine blade in which a variation between maximum and minimum
aerodynamic torques due to wind speeds is equal to or less than a
predetermined value.
[0024] A fourth mode of the present invention relates to a load
measuring program applicable to a wind turbine in which a pitch
angle of a wind turbine blade is variable, and making a computer
execute: a first process of providing a function expressing a
relation between a distortion of the wind turbine blade and a load
on the wind turbine blade, and obtaining the load on the wind
turbine blade by applying to the function a distortion based on
measurement data of the sensor; and a second process of calibrating
the function based on the measurement data of the sensor obtained
in a pitch angle range and a rotational speed range of the wind
turbine blade in which a variation between maximum and minimum
aerodynamic torques due to wind speeds is equal to or less than a
predetermined value.
[0025] A fifth mode of the present invention relates to a load
measuring method applicable to a wind turbine in which a pitch
angle of a wind turbine blade is variable, the method including:
providing a function expressing a relation between a distortion of
the wind turbine blade and a load on the wind turbine blade, and
obtaining the load on the wind turbine blade by applying to the
function a distortion based on measurement data of the sensor; and
calibrating the function based on respective measurement data of
the sensor obtained when the pitch angle is set to minimum and
maximum pitch angles in two points of a first azimuth angle and a
second azimuth angle different from the first azimuth angle by 180
degrees in a case where a wind speed is equal to or less than three
meters per second.
[0026] A sixth mode of the present invention relates to a load
measuring program applicable to a wind turbine in which a pitch
angle of a wind turbine blade is variable, and making a computer
execute: a first process of providing a function expressing a
relation between a distortion of the wind turbine blade and a load
on the wind turbine blade, and obtaining the load on the wind
turbine blade by applying to the function a distortion based on
measurement data of the sensor; and a second process of calibrating
the function based on respective measurement data of the sensor
obtained when the pitch angle is set to minimum and maximum pitch
angles in two points of a first azimuth angle and a second azimuth
angle different from the first azimuth angle by 180 degrees in a
case where a wind speed is equal to or less than three meters per
second.
[0027] According to the present invention, there is an effect that
a load on a wind turbine blade can be efficiently calibrated
regardless of observation conditions.
[0028] Still other objects and advantages of the present invention
will become readily apparent to those skilled in the art from the
following detailed description, wherein the preferred embodiments
of the invention are shown and described, simply by way of
illustration of the best mode contemplated of carrying out the
invention. As will be realized, the invention is capable of other
and different embodiments, and its several details are capable of
modifications in various obvious aspects, all without departing
from the invention. Accordingly, the drawings and description
thereof are to be regarded as illustrative in nature, and not as
restrictive.
BRIEF DESCRIPTION OF DRAWINGS
[0029] FIG. 1 Diagram showing a schematic configuration of an
entire wind turbine generator according to a first embodiment of
the present invention.
[0030] FIG. 2 Diagram for explaining a blade root part.
[0031] FIG. 3 An example of a cross section in a position of 1.8
meters from the root part of a wind turbine blade.
[0032] FIG. 4 Diagram for explaining arrangement of a sensor
position seen from the blade root part.
[0033] FIG. 5 Block diagram showing a schematic configuration of a
load measuring apparatus according to the first embodiment of the
present invention.
[0034] FIG. 6 Diagram showing the relations among aerodynamic
torque, generator rotational speed, and pitch angle at respective
wind speeds.
[0035] FIG. 7 Diagram showing an example of a table of a
calibration unit.
[0036] FIG. 8 Diagram for explaining an azimuth angle.
[0037] FIG. 9 Diagram of an example showing the relation between
distortion and load on the basis of measurement data.
[0038] FIG. 10 Diagram of an example showing the relation between
load and distortion wavelength in the blade root part.
[0039] FIG. 11A Diagram showing an example of comparison between
load (in the flap direction) and load in a calm state in a case
where calibration is performed with including measurement data of a
pitch angle in the range of a region A at a wind speed of 8 meters
per second.
[0040] FIG. 11B Diagram showing an example of comparison between
load (in the edge direction) and load in a calm state in the case
where calibration is performed with including measurement data of a
pitch angle in the range of the region A at a wind speed of 8
meters per second.
[0041] FIG. 12A Diagram showing an example of comparison between
load (in the flap direction) and load in a calm state in the case
where calibration is performed without including measurement data
of a pitch angle in the range of the region A at a wind speed of 8
meters per second.
[0042] FIG. 12B Diagram showing an example of comparison between
load (in the edge direction) and load in a calm state in the case
where calibration is performed without including measurement data
of a pitch angle in the range of the region A at a wind speed of 8
meters per second.
EXPLANATION OF REFERENCE
[0043] 1: wind turbine generator [0044] 7: sensor [0045] 20: load
calculating unit [0046] 30: calibration unit [0047] 31: table
[0048] 32: load obtaining unit [0049] 33: distortion calculating
unit [0050] 34: parameter calculating unit [0051] 100: load
measuring apparatus
BEST MODE FOR CARRYING OUT THE INVENTION
[0052] An embodiment of a load measuring apparatus, method, and
program according to the present invention will be described below
with reference to the drawings.
First Embodiment
[0053] FIG. 1 is a diagram showing a schematic configuration of a
wind turbine generator to which a load measuring apparatus 100
according to the present embodiment is applied. A wind turbine
generator 1 according to the present embodiment is a wind turbine
in which a pitch angle of a wind turbine blade 10 is variable.
[0054] The wind turbine generator 1 includes, as shown in FIG. 1, a
support 2, a nacelle 3 mounted on the upper end of the support 2,
and a rotor head (hub) 4 provided to the nacelle 3 so as to be
rotatable about an almost horizontal axis. To the rotor head 4,
three wind turbine blades 10 are radially attached about the
rotational axis of the rotor head 4. With the configuration, the
force of wind hitting the wind turbine blade 10 from the rotational
axis direction of the rotor head 4 is converted to power for
rotating the rotor head 4 about the rotational axis, and this power
is converted to electric energy by a generator.
[0055] Each of the wind turbine blades 10 is provided with a
plurality of sensors (sensing units) 7 for obtaining a distortion
of the wind turbine blade 10. The sensor 7 is, for example, an FBG
sensor (Fiber Bragg Grating sensor). The FBG is an optical fiber
sensor in which Bragg grating is formed and detects a change in
grating spacing caused by distortion and thermal expansion based on
a change in wavelength of reflected light.
[0056] The rotor head 4 also has a signal processor (not shown) for
receiving a measurement result in the sensor 7 (sensing unit).
[0057] Concretely, each wind turbine blade 10 is provided with
first, second, and third sensors. Each of the first, second, and
third sensors has a pair of sensors provided in opposite positions
sandwiching the wind turbine blade 10. Preferably, the first and
second sensors are provided so that a straight line connecting the
two sensors constructing the first sensor and a straight line
connecting the two sensors constructing the second sensor cross
almost perpendicular to each other. The third sensor is, for
example, a sensor used for temperature compensation and is provided
in the periphery of the first or second sensor.
[0058] FIG. 2 is a diagram for explaining the position of the
sensor 7 (sensing unit) attached to the wind turbine blade. As
shown in FIG. 2, in the present embodiment, the sensor 7 is
provided, for example, in a position away from the root of the wind
turbine blade 10 by 1.8 meters. The root corresponds to the border
between the wind turbine blade 10 and the rotor head 4 as shown in
FIG. 2. In the present embodiment, the root will be called the
"blade root part".
[0059] FIG. 3 is a cross section in the position away by 1.8 meters
from the blade root part of the wind turbine blade 10 to which the
sensor 7 is attached. In FIG. 3, a sensor A3 is provided on a back
side 21 of the wind turbine blade 10, and a sensor A1 is provided
on a ventral side 22, thereby constructing the first sensor. A
sensor A5 is provided in the same position as A3, and a sensor A6
is provided in the same position as A1, thereby constructing the
third sensor. A sensor A2 is provided in the direction of a front
edge 23 of the wind turbine blade 10, and a sensor A4 is provided
in the direction of a rear edge 24, thereby constructing the second
sensor.
[0060] FIG. 4 is a diagram schematically showing arrangement of the
sensors 7 attached to the wind turbine blade 10 viewed from the
blade root part of the wind turbine blade 10. As shown in FIG. 4,
in the present embodiment, the position where the sensor A1 is
provided is defined as HP, the position where the sensor A3 is
provided is defined as LP, the position where the sensor A2 is
provided is defined as LE, and the position where the sensor A4 is
provided is defined as TE. In FIG. 4, a tilt angle indicates tilt
of a plane of rotation of the wind turbine blade 10 with respect to
the vertical axis of a tower. Such a tilt angle is provided to
prevent the wind turbine blade 10 and the tower from being in
contact with each other even when the wind turbine blade 10 is
deformed by a wind force at the time of operation. The tilt angle
may be ignored in calculation which will be described later, or may
be taken into consideration.
[0061] Next, the configuration of the load measuring apparatus 100
according to the present embodiment will be described in
detail.
[0062] FIG. 5 is a functional block diagram showing functions of
the load measuring apparatus 100 which are illustrated in an
expanded manner.
[0063] As shown in FIG. 5, the load measuring apparatus 100
according to the present embodiment has a load calculating unit
(load calculating means) 20 and a calibration unit (calibration
means) 30.
[0064] The load calculating unit 20 has a function expressing the
relation between a distortion of the wind turbine blade and a load
on the wind turbine blade 10 and, by using the distortion based on
measurement data of the sensors A1 to A6 to the function, obtains
the load on the wind turbine blade 10.
[0065] The calibration unit 30 calibrates the function on the basis
of the measurement data of the sensors obtained in the pitch angle
range and the rotational speed range of the wind turbine blade 10
in which a variation between the maximum and minimum aerodynamic
torques by wind speed becomes a predetermined value or less. It is
more preferable to use measurement data of the sensors obtained in
a period satisfying conditions of the pitch angle range and
conditions of the rotational speed range of the wind turbine blade
10 in which the aerodynamic torque becomes a predetermined value or
less.
[0066] The measurement data of the sensors used for calibration of
the function by the calibration unit 30 will be described
concretely.
[0067] FIG. 6 is a diagram showing changes in aerodynamic torque by
wind speeds (from 4 meters per second to 12 meters per second of
wind speed) while the wind turbine blade 10 is changed from a fine
side (pitch angle of 21 degrees) to a feather side (pitch angle of
109 degrees) until the wind turbine blade 10 is stopped. The pitch
angles of 21 degrees and 109 degrees indicate angles of the wind
turbine blade 10 in a case where the position of a blade reference
line determined upon attachment of the wind turbine blade 10 to the
wind turbine rotor 3 is defined as 0 angle. The pitch angle of 0
degree is an angle on the blade reference line defined in a blade
cross section, and an angle formed by this line and the rotor plane
is a pitch angle.
[0068] To obtain FIG. 6, the three wind turbine blades 10 are
simultaneously changed at a velocity of 2.5 degrees per second in
the range where the pitch angle is 21 degrees to 45 degrees, and at
a velocity of 1.0 degree per second in the range where the pitch
angle is 45 degrees to 109 degrees, and measurement data of the
three wind turbine blades 10 is obtained. The wind turbine blades
10 are rotated by changing the pitch angle and are in an idle
state. The idle state is a state where the wind turbine blades 10
are rotated in a range of the wind turbine generator 1 not
generating power (for example, a state where the wind turbine
blades 10 rotate at a low speed).
[0069] Since similar processes are performed on all of the three
wind turbine blades 10, in the following, description will be made
on one wind turbine blade 10.
[0070] As shown in FIG. 6, a region A includes a period in which
the wind turbine generator generates power and a period in which an
aerodynamic brake as a force for stopping rotation of a rotor is
strongly applied by opening the pitch angle to a feather side for
stop or the like. As shown in FIG. 6, in the region A, there is
applied an aerodynamic torque which varies according to wind speed.
After that, on the right side of the region A (in other words, in
the case where the pitch angle is larger than 60 degrees and the
rotational speed of the generator is 0 to 300 rpm (at a frequency
of 60 Hz)), the value of torque is approximately -300
kilo-newton-meters or more at any wind speed, which is such a small
torque that the influence of the aerodynamic torque can be
ignored.
[0071] In FIG. 6, the condition of the rotational speed range on
the right side of the region A is 0 to 300 rpm. However, the
present invention is not limited to this condition. The condition
may be set according to frequency. For example, in a case of 50 Hz,
the condition of the rotational speed range may be set to 0 to 250
rpm.
[0072] As described above, the calibration unit 30 uses measurement
data obtained in the region other than the region A, that is, in
the range where the aerodynamic torque does not depend on wind
speed. In other words, used is measurement data obtained in the
range of 60 degrees to 109 degrees of the pitch angle, as the pitch
angle in the range where the variation between the maximum and
minimum aerodynamic torques is equal to or less than a
predetermined value. The reason for using data in the region other
than the region A will be described later.
[0073] More concretely, the calibration unit 30 has a table 31, a
load obtaining unit (load obtaining means) 32, a distortion
calculating unit (distortion calculating means) 33, and a parameter
calculating unit 34.
[0074] The calibration unit 30 obtains measurement data of the
sensor 7 in a no-load state on the basis of the load on the wind
turbine blade 10 obtained by the load obtaining unit 32 and
measurement data of the sensor 7, and performs offset calibration
on the measurement data of the sensor 7 by using the measurement
data in the no-load state. By this operation, in consideration of a
measurement error included in the sensor 7 itself, precision of the
calibration can be improved.
[0075] In the table 31, the load on the blade root part of the wind
turbine blade 10, the pitch angle of the wind turbine blade 10, and
the azimuth angle thereof in a calm state (an ideal environment
condition for calibration) are associated with one another. For
example, the table 31 is provided as a list (table) shown in FIG.
7, in which stored are values .alpha..sub.1, .alpha..sub.2,
.alpha..sub.3, .alpha..sub.4, . . . of the load on the blade root
part associated with the combination of the azimuth value and the
pitch angle of the wind turbine blade 10.
[0076] The azimuth angle is, as shown in FIG. 8, an angle formed by
a predetermined reference and the axis of the wind turbine blade 10
in the plane of rotation of the wind turbine blade 10, and in the
present embodiment, the reference is set in a state where the wind
turbine blade 10 is positioned at the highest position. Therefore,
the azimuth angle with the wind turbine blade 10 being positioned
at the highest part of the wind turbine is zero degree, and the
azimuth angle with the wind turbine blade 10 being positioned at
the lowest part is 180 degrees.
[0077] In the list (table) as shown in FIG. 7, a moment in the
blade root part can be obtained by calculating each of moments by
deadweights in the positions of the sensors A1 to A4 according to
the following equation (1) and coordinate-converting these
moments.
M=9.8.times.W.times.l.sub.g.times.sin .theta.cos .beta. [Nm]
(1)
[0078] In the equation (1), W denotes the weight of the wind
turbine blade 10, I.sub.g denotes the position of the center of
gravity measured from the blade root part of the wind turbine blade
10 (which is a known value at the stage of manufacture), .theta.
indicates a function between the azimuth angle and the tilt angle,
and .beta. expresses a function between the pitch angle and the
tilt angle.
[0079] The load obtaining unit 32 obtains from the table 31 the
load on the blade root part of the wind turbine blade 10
corresponding to the pitch angle and the azimuth angle of the wind
turbine blade 10 when measurement data is obtained by the sensor
7.
[0080] The distortion calculating unit 33 calculates distortion of
the wind turbine blade 10 from the measurement data of the sensor
7. Concretely, the distortion calculating unit 33 extracts a
distortion wavelength from the measurement data of the sensor 7,
and converts the distortion wavelength to a distortion on the basis
of a predetermined function. More concretely, the distortion
wavelength data in the measurement data of the sensor 7 is
converted to a numerical value by a not-shown signal processor
provided at the rotor head 4. The distortion wavelength obtained as
the numerical value is converted to a distortion .epsilon.. The
distortion .epsilon. is obtained by the following equation (2).
.epsilon.=P.sub.e{(.lamda.-.lamda..sub.i)-.alpha.(.lamda..sub.T-.lamda..-
sub.Ti)} (2)
[0081] In the equation (2), .lamda. denotes measurement data
obtained by the first sensor (second sensor), .lamda..sub.i denotes
measurement data in the no-load state obtained by the first sensor
(second sensor), .lamda..sub.T denotes measurement data obtained by
the third sensor, .lamda..sub.Ti denotes calculation data in the
no-load state obtained by the third sensor, p.sub.e indicates a
distortion optical constant (809 .mu..epsilon./nm), and a indicates
a temperature compensation coefficient (2. 2). .lamda..sub.i is an
average value of measurement data and is obtained by the following
equation.
.lamda..sub.i=(.lamda..sub.max+.lamda..sub.min)/2 (3)
[0082] In the equation (3), .lamda..sub.max denotes the maximum
peak value of data, and .lamda..sub.min denotes the minimum peak
value.
[0083] Since a distortion is calculated in each of the sensors A1
and A3 constructing the first sensor as well as each of the sensors
A2 and A4 constructing the second sensor as described above, four
distortions are calculated. Further, by calculating the difference
between the distortions obtained by the sensors A1 and A3
constructing the first sensor, a distortion .epsilon..sub.F in the
flap direction (the HP-LP direction in FIG. 4) of the wind turbine
blade 10 is calculated. By calculating the difference between the
distortions obtained by the sensors A2 and A4 constructing the
second sensor, a distortion .epsilon..sub.E in the edge direction
(the LE-TE direction in FIG. 4) of the wind turbine blade 10 is
calculated.
[0084] The parameter calculating unit 34 calibrates a parameter of
a function on the basis of the relation between the load on the
wind turbine blade 10 obtained by the load obtaining unit 32 and
the distortion calculated by the distortion calculating unit 33.
Concretely, a new function is constructed on the basis of the
relation among distortions .epsilon..sub.F and .epsilon..sub.E and
a load on the blade root part of the wind turbine blade 10
associated with the azimuth angle and the pitch angle at a timing
of obtaining measurement data as original data based on which
distortions .epsilon..sub.F and .epsilon..sub.E are calculated. By
using a coefficient of the new function, the coefficient of the
function in the load calculating unit 20 is calibrated. One new
function is generated in the flap direction, and another one new
function is generated in the edge direction.
[0085] For example, to convert the distortion .epsilon. to a moment
in the position of the sensor, the following equation (4) is used.
"d" denotes the inner diameter of the wind turbine blade 10 in the
mount position (1.8 meters away from the blade root part) of the
sensor 7, L denotes number of the wind turbine blade 10 (L=1, 2,
3), E denotes Young's modulus of the blade material (FRP), I
denotes a second moment of area in the mount position of the
sensor, M.sub.sensor denotes a bending moment (load) in the sensor
mount position, .epsilon..sub.2L-1 and .epsilon..sub.2L denote
distortions based on the measurement data of the pair of sensors
(the first or second sensor), and .epsilon..sub.2L-1,0 and
.epsilon..sub.2L,0 are initial values of distortions of the first
or second sensor.
[ Mathematical Expression 1 ] M sensor = EI d { ( 2 L - 1 - 2 L ) -
( 2 L - 1 , 0 - 2 L , 0 ) } .times. 10 - 6 ( 4 ) ##EQU00001##
[0086] Regarding this moment, when the ratio between a moment
M.sub.root in the blade root part of the wind turbine blade 10 and
the moment M.sub.sensor in the mount position of the sensor 7 (for
example, the position away from the blade root part of the wind
turbine blade 10 by 1.8 m) is set as .beta. (>1), the following
equation is obtained.
[ Mathemetical Expression 2 ] M root = .beta. M sensor = .beta. EI
d { ( 2 L - 1 - 2 L ) - ( 2 L - 1 , 0 - 2 L , 0 ) } .times. 10 - 6
= a ( 2 L - 1 - 2 L ) .times. 10 - 6 + b [ Nm ] ( 5 ) where a =
.beta. EI d [ Nm ] ( 6 ) b = - .beta. EI d ( 2 L - 1 , 0 - 2 L , 0
) .times. 10 - 6 [ Nm ] ( 7 ) ##EQU00002##
[0087] As shown in the equation (5), the moment M.sub.root in the
blade root part is expressed as a linear function using
coefficients "a" and "b" as parameters and using distortions of the
pair of sensors (the first or second sensor) as variations.
[0088] Consequently, in a case of generating a graph of the moment
M.sub.root with a distortion .epsilon..sub.F or .epsilon..sub.E on
the horizontal axis and the azimuth angle and pitch angle on the
vertical axis, by calculating a gradient "a" and an intercept "b"
obtained on the basis of the linear function, the coefficients "a"
and "b" can be calculated as parameters.
[0089] A method of forming a graph of the linear function will be
described in the following.
[0090] A graph is formed by setting the distortion .epsilon..sub.F
in the flap direction and the distortion .epsilon..sub.E in the
edge direction in each of the wind turbine blades 10 on the
horizontal axis and setting the load (moment) M.sub.root
corresponding to the distortions .epsilon..sub.F and
.epsilon..sub.E obtained from the table 31 on the vertical axis,
and the tilt "a" and the intercept "b" are extracted from the
graph. More concretely, a graph shown in FIG. 9 is generated. On
the basis of such a graph, the coefficients "a" and "b" in the case
of the flap direction of each of the wind turbine blades 10 and the
coefficients "a" and "b" in the case of the edge direction are
calculated. For example, as a parameter in the flap direction in
the first wind turbine blade 10#1, there are set
a=2.014.times.10.sup.9 and b=-0.448.times.10.sup.3. Similarly, for
each of the wind turbine blades 10#2 and 10#3, the coefficients "a"
and "b" in the flap direction and in the edge direction are
calculated.
[0091] The parameter calculating unit 34 calculates the
coefficients "a" and "b" as described above and then outputs them
to the load calculating unit 20. With the above, the parameters of
the function of the load calculating unit 20 are calibrated. By
applying measurement data obtained from the sensor to the function
of the load calculating unit 20, the obtained moment in the blade
root part is calibrated.
[0092] Next, the actions of the calibration unit 30 of the load
measuring apparatus according to the present embodiment will be
described. Since processes performed on each of the wind turbine
blades 10 are the same, in the following description, the processes
on one wind turbine blade 10 will be described as an example.
[0093] First, in the present embodiment, the pitch angle is changed
from 60 degrees to 109 degrees, and measurement data of the sensors
A1 to A6 is obtained. The measurement data is provided to the load
obtaining unit 32 of the calibration unit 30.
[0094] The load obtaining unit 32 refers to the table 31 and reads
the load on the blade root part associated with the information on
the azimuth angle and the pitch angle of the measurement data
obtained by the sensors A1 to A6. Subsequently, the load obtaining
unit 32 generates a graph showing the measurement data of each of
the sensors on the vertical axis and the load on the blade root
part on the horizontal axis for each of the sensors (see FIG. 10)
and, from the graphs, reads the distortion wavelength when the
value of the load on the horizontal axis is "0". This value
corresponds to measurement data of the sensor in the no-load state,
that is, the offset value of each sensor. The charge obtaining unit
32 outputs to the distortion calculating unit 33, together with the
offset values of the sensors, information on the load on the blade
root part read from the table 31 and data of the sensors when the
load is obtained. By obtaining the offset values of the sensors by
the charge obtaining unit 32 as described above, in the following
processes, a measurement error included in the sensor itself is
calibrated, and thus measurement precision of the load can be
improved.
[0095] The distortion calculating unit 33 extracts the distortion
wavelengths from the measurement data of the sensors A1 to A6 and,
on the basis of the measurement data calculated by the sensors and
the measurement data in the no-load state, calculates the
distortion (deadweight moment) .epsilon. in each sensor position by
using the equation (2). For example, a distortion .epsilon..sub.A1
in the sensor A1 is obtained by the following equation (2)'.
.epsilon..sub.A1=P.sub.e{(.lamda..sub.HP-.lamda..sub.HPi)-.alpha.(.lamda-
..sub.HPT-.lamda..sub.HPTi)} (2)'
[0096] In the equation (2)', .lamda..sub.HP denotes distortion
wavelength data of the sensor A1, .lamda..sub.HPT denotes
distortion wavelength data of the sensor A5 for temperature
compensation mounted in the periphery of the sensor A1,
.lamda..sub.HPT denotes the offset value (measurement data in the
no-load state) of the sensor A1, and .lamda..sub.HPTi indicates the
offset value (measurement data in the no-load state) of the sensor
A5.
[0097] The distortion calculating unit 33 calculates the distortion
.epsilon. for each of the sensors A3, A2, and A4 by similar
calculating processes. As a result, total four distortions
.epsilon..sub.A1, .epsilon..sub.A2, .epsilon..sub.A3, and
.epsilon..sub.A4 are calculated. After calculating the distortions
.epsilon..sub.A1 to .epsilon..sub.A4 for the sensors A1 to A4, the
distortion calculating unit 33 outputs the values and information
on the load on the blade root part inputted from the load obtaining
unit 32 to the parameter calculating unit 34.
[0098] On the basis of the relation between the distortions
.epsilon..sub.A1 to .epsilon..sub.A4 for the respective sensors and
the information on the load on the blade root part inputted from
the load obtaining unit 32, the parameter calculating unit 34
calibrates parameters of a function expressing the relation between
the distortion of the wind turbine blade 10 and the load on the
blade root part of the wind turbine blade 10.
[0099] Concretely, the relational expression between information on
the load on the blade root part of the wind turbine blade 10 and
the distortion of the wind turbine blade 10 is shown as the above
equation (5). To be concrete, one relational expression is obtained
for the first sensor, and another one relational expression is
obtained for the second sensor. Therefore, two relational
expressions are generated for one wind turbine blade 10. For
example, the relational expression for the first sensor is shown as
follows.
M.sub.HP-LP=a(.epsilon..sub.A1-.epsilon..sub.A3).times.10.sup.-6+b
[Nm] (5)'
[0100] In the equation (5)', .epsilon..sub.A1 denotes the
distortion in the position of the sensor A1 calculated on the basis
of the equation (2)', and .epsilon..sub.A3 denotes the distortion
in the position of the sensor A3 calculated on the basis of a
similar calculation equation.
[0101] When the difference .epsilon..sub.A1=.epsilon..sub.A3
between the distortions in the flap direction in the equation (5)'
(the HP-LP direction in FIG. 4) is set on the horizontal axis and
M.sub.HP-LP is set on the vertical axis, a graph as shown in FIG. 9
is obtained. By expressing the relation between the distortions
.epsilon..sub.A1 to .epsilon..sub.A4 and the information on the
load on the blade root part in the form of a graph in this way, the
intercept and the tilt of the graph can be derived, and the
coefficient "a" (tilt) and the coefficient "b" (intercept) in the
equation (5)' can be calculated. Two combinations of the
coefficients "a" and "b" in each of the flap direction and the edge
direction are calculated for one wind turbine blade 10.
[0102] By repeatedly performing the processes from measurement by
the sensor to calculation of the coefficients, a plurality of
coefficients is obtained. By using an average value of the
coefficients, a calibrated relational expression is obtained. For
example, by eliminating the maximum and minimum values, data in
which noise suddenly occurs can be eliminated. Even when data which
does not include noise is eliminated, no influence is exerted on
calculation of an average value.
[0103] After obtaining the very reliable relational expression, in
other words, the calibrated relational expression, the load
calculating unit 32 calculates the load on the blade root part of
the wind turbine blade 10 from the measurement data of the sensors
by using the relational expression. In such a manner, a very
reliable load can be calculated.
[0104] In the present embodiment, data in the region other than the
region A in FIG. 6 is used out of measurement data measured by the
sensors A1 to A6, which is to improve precision of the calibration.
Concretely, upon obtaining the coefficients "a" and "b",
approximation to a moment obtained in the calm state (ideal moment
for performing calibration) is performed. It will be described more
concretely with reference to FIGS. 11A and 11B as well as FIGS. 12A
and 12B.
[0105] FIG. 11A shows moments in the flap direction in the calm
state on the horizontal axis, and moments in the flap direction in
a case of a wind speed of eight meters on the vertical axis.
Similarly, FIG. 11B shows comparison of the moments in the edge
direction. FIGS. 11A and 11B show the functions obtained in the
case of obtaining the coefficients "a" and "b" by using the
measurement data including the region A, and are compared with the
ideal data in the calm state. The ideal function in the calm state
is expressed as y=x. When the coefficients "a" and "b" are
calculated by using the measurement data including the region A,
y=0.9701x -31.88 is obtained. When the moment in the calm state and
the moment calculated from the measurement data including the
region A are compared with each other, many points exist in
positions deviated from y=x. It shows that an error in the loads
obtained by using the coefficients "a" and "b" calculated while
including the measurement data of the region A is larger than that
in the loads in the calm state.
[0106] On the other hand, similarly to FIGS. 11A and 11B, FIGS. 12A
and 12B show moments in the calm state on the horizontal axis and
moments in the case of a wind speed of eight meters on the vertical
axis, in a case of calculating the coefficients "a" and "b" by
using measurement data excluding the measurement data obtained in
the region A in FIG. 6. For example, as shown in FIG. 12A, in the
case of calculating the coefficients "a" and "b" by using the
measurement data without including the region A, y=0.9968x -3.322
is obtained. In the result of the loads thus obtained, as being
obvious from the graph, the moments in the calm state and those in
the case of the wind speed of eight meters almost coincide with
each other. By calibrating the function with the coefficients "a"
and "b" obtained without including the measurement data in the
region A, the load can be more approximated to the load in the calm
state.
[0107] In the case of obtaining measurement data by the sensors, it
is sufficient to rotate the wind turbine blade 10 at least once
from the azimuth angle of zero degree to 180 degree. One data file
for calibration is generated by rotation of 180 degrees. However,
the present invention is not limited to the number of rotation
according to the azimuth angle. In the present embodiment, one data
file for calibration is generated by rotation of 360 degrees.
[0108] More concretely, by moving the pitch angle from 109 degrees
to 60 degrees or from 60 degrees to 109 degrees, the rotor starts
idling. By moving the pitch angle from 109 degrees to 60 degrees,
the rotor is rotated at least once, and thus one data file is
obtained. Similarly, by moving the pitch angle from 60 degrees to
109 degrees, the rotor is rotated at least once and thus one data
file is obtained.
[0109] In other words, in the present embodiment, in the range
exclusive of the aerodynamic influence, at the time of moving the
pitch angle to the fine side, one data file for calibration is
obtained under the condition that the rotor rotates at least once.
Similarly, at the time of moving the pitch angle to the feather
side, one data file for calibration is obtained.
[0110] In the present embodiment, by performing the pitch angle
operation as described above, ten data files for calibration are
obtained.
[0111] Further, in the case where calibration data for ten times
(that is, the coefficients "a" and "b") is calculated, reliability
of the coefficients "a" and "b" is preferably verified by
calculating the average value of the data.
[0112] X denotes data for calibration (18 pieces of measurement
data in the calm state and 12 pieces of calibration data (data in
the edge direction and the flap direction of each of the wind
turbine blades 10), and N denotes the number of times of moving the
pitch angle from 109 degrees to 60 degrees and to 109 degrees (one
cycle). "m" denotes an average value. In this case, the maximum and
minimum data is eliminated from 2N pieces of calibration data
files, and an average value of 2(N-1) files is obtained. Whether
the average value of each calibration values "a" and "b" satisfies
the following range condition or not is verified. In the case where
the average value satisfies a reference value, the average value of
the calibration data is set as an on-site parameter.
[ Mathematical Expression 3 ] Average value m = n = 1 2 ( N - 1 ) X
n 2 ( N - 1 ) ( 8 ) ##EQU00003##
[0113] Average Value
[0114] Verification of Reference Value
1.7.times.10.sup.9<a<2.7.times.10.sup.9 (9)
-100 kNm<b<100 kNm (10)
[0115] As described above, measurement data is obtained by the
sensors provided to the wind turbine blades 10 and, on the basis of
the obtained data, distortions and loads of the wind turbine blades
10 are calculated. A function stored in the load calculating unit
20 is calibrated with coefficients of a new function obtained from
the relation between the distortion and the load of the wind
turbine blade 10 calculated on the basis of the measurement data.
Since a new function is easily calculated from the measurement
data, the coefficients for calibration can be easily
determined.
[0116] Used at this time is measurement data of the sensor obtained
in the pitch angle range of the wind turbine blade 10 in which the
variation between the maximum and minimum aerodynamic torques is
equal to or less than a predetermined value. Since measurement data
in which the influence of the aerodynamic torque can be ignored is
used, precision of the calibration can be improved.
[0117] By calculating a distortion of a sensor itself and
offsetting it, precision of the calibration can be further
improved. Further, measurement data may be obtained in the pitch
angle range of the wind turbine blade 10 (for example, the range of
the pitch angle from 60 degrees to 109 degrees) in which the
variation between the maximum and minimum aerodynamic torques is
equal to or less than a predetermined value. The measurement data
is not limited particularly to the azimuth angle. Therefore,
measurement data in a wide range can be used for calibration.
[0118] Since acquisition of measurement data, calculation of a load
and a distortion, and verification of reliability of calibration
data are performed by the load measuring apparatus 100, time
required for the calibration work can be shortened, and the burden
on the user can be reduced.
[0119] In the above-described embodiment, processing performed by
hardware is assumed as the load measuring apparatus. However, the
present invention does not have to be limited to such a
configuration. For example, there may be employed a configuration
for processing by software on the basis of output signals from the
sensors. In this case, the load measuring apparatus includes a CPU,
a main storage such as a RAM, and a computer-readable recording
medium on which a program for realizing all or part of the
processing is recorded. The CPU reads the program recorded on the
recording medium and executes processing/computing of information,
thereby realizing processing similar to that of the above-described
load measuring apparatus.
[0120] The computer-readable recording medium is a magnetic disk, a
magnetooptical disk, a CD-ROM, a DVD-ROM, a semiconductor memory,
or the like. It is also possible to distribute this computer
program to a computer via a communication line and execute it by
the computer to which the program is distributed.
MODIFICATIONS
[0121] In the load measuring apparatus 100 according to the present
embodiment, the function is calibrated on the basis of measurement
data of the sensor obtained in the pitch angle range of the wind
turbine blade 10 in which the variation between the maximum and
minimum aerodynamic torques is equal to or less than a
predetermined value. However, the present invention is not limited
to the above. For example, it is also possible to set the range of
the rotational speed of the wind turbine blade 10 in place of the
pitch angle range and calibrate the function on the basis of data
of the sensor obtained in the range of the rotational speed of the
wind turbine blade in which the variation between the maximum and
minimum aerodynamic torques due to wind speeds is equal to or less
than a predetermined value.
[0122] Although the number of the plurality of wind turbine blades
10 is three in the wind turbine generator 1 according to the
present embodiment, the number of wind turbine blades 10 is not
particularly limited.
[0123] In the load measuring apparatus 100 according to the present
embodiment, the number of the sensors attached to one wind turbine
blade 10 is six. However, the number of sensors is not particularly
limited.
[0124] In the load measuring apparatus 100 according to the present
embodiment, the table 31 is obtained by calculation by using the
azimuth angle and the pitch angle. However, the present invention
is not limited to the present embodiment. For example, a table may
be provided in advance to the calibration unit 30.
Second Embodiment
[0125] Next, a second embodiment of the present invention will be
described.
[0126] The difference in the load measuring apparatus of the
present embodiment from the first embodiment is that data is
obtained such that angle data of the azimuth angle and the pitch
angle is limited to predetermined values and wind speeds are
limited to a range in which negative aerodynamic torques are small.
In the following, with respect to the load measuring apparatus
according to the present embodiment, the points common to the first
embodiment will not be described and different points will be
mainly described.
[0127] When the wind speed is three meters or less, the sensor 7
obtains measurement data when the pitch angle is set to the minimum
and maximum pitch angles at two points of a first azimuth angle and
a second azimuth angle turned by 180 degrees from the first azimuth
angle.
[0128] More concretely, the sensor obtains measurement data in the
case where the wind speed is three meters or less, the azimuth
angles of the wind turbine blade 10 are 90 degrees and 270 degrees,
and the pitch angles at the respective azimuth angles are set to 21
degrees and 109 degrees.
[0129] In the case of measuring data of one wind turbine blade 10,
the pitch angles of the other two wind turbine blades 10 are set
to, for example, 85 degrees or the like so as to be an idle
state.
[0130] By using the data measured at two points in positions of the
azimuth angles different from each other by 180 degrees, as
measurement data used for the function calculated by the parameter
calculating unit 34, data of a wide range with respect to the
horizontal axis can be obtained. Thus improved is precision in the
case of calculating the coefficients "a" and "b" from small
measurement data. Since the parameters can be calculated from small
measurement data, time required for calibration can be
shortened.
[0131] Although the embodiments of the present invention have been
described above in detail with reference to the drawings, concrete
configurations are not limited to these embodiments. Design changes
and the like in the range not departing from the gist of the
present invention are also included therein.
[0132] It will be readily seen by one of ordinary skill in the art
that the present invention fulfils all of the objects set forth
above. After reading the foregoing specification, one of ordinary
skill in the art will be able to affect various changes,
substitutions of equivalents and various aspects of the invention
as broadly disclosed herein. It is therefore intended that the
protection granted hereon be limited only by definition contained
in the appended claims and equivalents thereof.
* * * * *